International Patent Publication No. WO 92/22554 discloses a series of sigma receptor ligands which are considered useful for the treatment of a range of psychic and neurological disorders. The structure activity relationship of these compounds has been further investigated by Perregaard, J. et al., J. Med. Chem. 1995, 38, 11, p. 1998-2008.
One of the compounds herein, which is the subject of the present invention, has the general formula 
This compound was shown in Perregaard, J. et al., J. Med. Chem. 1995, 38, 11, p. 1998-2008 to be a potent and selective sigma ligand. Furthermore, the anxiolytic potential of the compound was tested in the black/white exploration test in rats, which is an animal model predictive for anxiolytic activity, and was found to be active over a large dose range.
Evidence has been presented from studies of the biology and function of sigma receptors that sigma receptor ligands may be useful in the treatment of a range of psychic and neurological disorders, including psychosis and movement disorders, such as dystonia and tardive dyskinesia, and motor disturbances associated with Huntington's chorea or Tourette's syndrome and in Parkinson's disease (Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355). The known sigma receptor ligand rimcazole clinically shows effect in the treatment of psychoses (Snyder, S. H., Largent, B. L. J. Neuropsychiatry 1989, 1, 7) and a group of sigma receptor ligands have been described to show antihallucinogenic activity in animal models (International Patent Publication No. WO 9103243).
Sigma receptor ligands have also been reported to be involved in modulation of NMDA receptor mediated events in the brain and to act as anti-ischemic agents in in vivo tests (Rao, T. S. et al, Molecular Pharmacology, 1990, 37, 978). In addition to ischemia they may also be useful in the treatment of other such NMDA receptor mediated events, e.g. epilepsy and convulsion.
Also, some sigma receptor ligands have been found to show anti-amnesic effects in an animal model (Early et al., Brain Research 1991, 546, 281-286).
Sigma ligands have been shown to influence central acetylcholine levels in animal models (Matsuno et al, Brain Research 1992, 575, 315-319; Junien et al, Eur. J. Pharm. 1991, 200, 343-345) and may therefore have potential in the treatment of senile dementia of the Alzheimer type.
Finally, some guanidine derivatives having sigma receptor activity have been disclosed to be useful as anxiolytics (International Patent Publication No. WO 9014067).
Accordingly, a compound which acts potently on the sigma receptors in the central nervous system is believed to be of potential use in the treatment of anxiety, psychosis, epilepsy, convulsion, movement disorders, motor disturbances, amnesia, cerebrovascular diseases, senile dementia of Alzheimer type and Parkinson's disease.
The free base of 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine] is an oil and as such not useful for the production of solid pharmaceutical preparations, such as tablets or capsules. As oral administration of a solid entity is the preferred and most convenient method for the administration of a pharmaceutical, a solid form of the compound, suitably a pharmaceutically acceptable salt thereof, which can be mixed with various adjuvants or diluents and formed into tablets or filled in capsules, is highly desirable.
The compound, 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine] was disclosed for the first time in International Patent Publication No. WO 92/22544 (compound No. 5a) in the form of the oxalic acid addition salt.
Another acid addition salt of 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine], namely the fumarate has been disclosed in Perregaard, J. et al., J. Med. Chem. 1995, 38, 11, p. 1998-2008.
The aqueous solubility of both the free base and the fumarate is very low, a property which is known to possibly compromise the bioavailability of the drug. Furthermore, experiments in rats and dogs have indicated a limited bioavailablity of the fumarate of 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine].
It has now, surprisingly, been found that the relative bioavailability of the hydrochloride of 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine] is three times larger than that of the fumarate salt.
The hydrochloride of the invention also have improved water solubility compared to the fumarate of 1′-[4-[1-(4-fluorophenyl)-1H-indole-3-yl]-1-butyl]-spiro[isobenzofuran-1(3H),4′-piperidine].